The relationship between membrane attachment and initiation of phage lambda DNA synthesis will be examined by infecting E. coli lysogenic for lambda ind- with radioactive lambda c17. At various intervals after infection, cells will be lysed and the percentage of phage DNA bound to a rapidly sedimenting membrane complex will be determined. Simultaneously, lysates will also be examined for the percentage of phage DNA that is in the form of a closed circular double- stranded duplex. This form of phage DNA is nicked by a putative endonuclease controlled by genes O and P of the phage. Since the products of genes O and P are also required for the initiation of phage DNA synthesis, it can be determined whether there is a temporal relationship between membrane binding and initiating of phage DNA synthesis. The question of whether transcription of the phage DNA is required for nicking will also be determined. For this, the rightward promoter mutant lambda X13 will be radioactively labeled by inducing the tandem lysogen C600 lambda int 6 1mm 434: lambda sus N7N52c1857). E. coli lysogenic for lambda c1857 will be infected with the mutant phage and destruction of closed circular phage DNA will be observed after prophage induction. The participation of a host function in the nicking of circular phage DNA will be examined by using gro-P bacterial mutants. These mutants cannot support the growth of lambda unless the phage is mutated in gene P. It will be determined whether circular DNA is nicked in the gene P mutants but not in the wild type phage.